Pregelatinized starches are physically modified starches which are predominantly produced by wet-thermal digestion. In contrast to native starch, they form dispersions or pastes or gels with cold water, depending on the concentration of the pregelatinized starch used and depending on the type of starch used to produce the pregelatinized starch. On account of there properties a number of possible applications result for pregelatinized starches in the food industry and moreover in many technical fields The use of pregelatinized starch, which is also termed cold-swelling starch, instead of native starch has in many cases the advantage that production processes can be simplified and shortened.
In principle it is possible to produce cold-swelling starch (pregelatinized starch) by various processes, for example by wet-thermal treatment using a roller dryer, mechanical and thermal treatment with an extruder or exclusively mechanical treatment with the vibratory mill. All processes share the fact that, via energy transfer processes which are not known in more detail the grown starch grain structure and the para-crystalline molecular organization is disrupted and the starch is converted into an amorphous substance. Since in the case of the known processes the operating variables differ from one another qualitatively and quantitatively, products having differing properties result therefrom.
Industrial pregelatinized starch production is principally carried out Musing the roller dryer. Generally, in this case an approximately 35% strength starch-water suspension is applied to the surface of a heated roller of the roller dryer. On the roller surface the starch is nor only gelatinized but also dehydrated.
In order to impart cold-swelling properties to starch, the grain structure or paracrystalline structure of the starch must be disrupted during heating on the roller dryer (for example for <1 minute at approximately 100° C.). This achieves an intermediate state between that of a solid and a completely soluble substance. Another possibility in that instead of the starch-water suspension, a precooked starch paste is applied to the roller for drying.
In addition, various variants of the roller drying process are described in which the pregelatinization is carried out in the presence of additives such as salts, acids, lipids, etc. Indoor in which chemically modified starches are used as starting material.
To produce, for example, instant desserts and instant puddings, pregelatinized starches are required which after stirring into cold liquid, for example water or milk, form sliceable gels within a short time, for example in the case of a boiled pudding. These requirements are not met by the commercial pregelatinized starches of wheat, potato or corn starch. To achieve the abovementioned properties, in the case of the previously commercially available pregelatinized starches, additives to the pregelatinized starch such as gelatin, alginate, carrageenan and/or inorganic salts are required.